1. Field of the Invention
The present general inventive concept relates to a side light-emitting device, a backlight unit using the side light-emitting device as a light source, and a liquid crystal display (LCD) apparatus employing the backlight unit.
2. Description of the Related Art
A liquid crystal display (LCD) is a non-emissive (i.e., passive) flat panel display that needs an external light source to produce an image, since the LCD itself does not emit light. A backlight unit is located behind the LCD and emits light.
Backlight units are classified as direct light type backlight units and edge light type backlight units according to the position in which a light source is arranged. For a direct light type backlight unit, a plurality of light sources disposed beneath an LCD directly emit light onto an LCD panel. For an edge light type backlight unit, a lamp located along an edge of a light guide panel (LGP) emits light onto the LCD panel via the LGP.
The direct light type backlight unit may use light-emitting diodes (LEDs) that emit Lambertian radiation as a point light source. When color light beams emitted by a LED are diffused by a diffusion plate to illuminate the LCD panel, a side-emitting LED that allows the light beams emitted from sides thereof to propagate in a slightly lateral direction and enter the diffusion plate is needed to prevent the color light beams emitted by the LED to be visible from above the diffusion plate.
FIG. 1 is a cross-sectional side view of a conventional side emitter 1 of a side-emitting LED disclosed in U.S. Pat. No. 6,679,621. Referring to FIG. 1, the conventional side emitter 1 includes a funnel-shaped reflecting surface 3 sloped with respect to a central axis c′, a first refracting surface 5 obliquely inclined with respect to the central axis c′ to refract light rays reflected by the reflecting surface 3, and a second refracting surface 7 extending as a convex curve from a bottom surface 9 to the first refracting surface 5.
Light that is emitted from a LED (not shown) into the bottom surface 9 of the conventional side emitter 1 and is incident on the reflecting surface 3 is reflected by the reflecting surface 3 to the first refracting surface 5 and is refracted by the first refracting surface 5 to exit the side emitter 1 in a substantially lateral direction. On the other hand, light that is emitted from the LED into the side emitter 1 and is incident on the second refracting surface 7 is transmitted through the second refracting surface 7 to exit the side emitter 1 in the substantially lateral direction.
In the conventional side-emitting LED, light propagating at about 10° upward from a horizontal axis has the highest intensity. Thus, light must be spread out over a wider area in order to obtain a slim backlight unit and an LCD having uniform screen brightness. However, the conventional side-emitting LED cannot satisfy this requirement.
Another drawback of the conventional side-emitting LED is that it is difficult to manufacture due to the complicated structure of the reflecting surface 3, the first refracting surface 5, and the second refracting surface 7 having a curved shape.